# Harness² vs Unstoppable

> Harness² scores 42 (E) to Unstoppable's 34.9 (F) for agent harnesses. Prices, MCP, x402, uptime and agent notes side by side.

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- Updated: 2026-10-28

Harness² scores 42 (E) on agent readiness against Unstoppable's 34.9 (F), and leads in 4 of 7 scored categories. Unstoppable leads on reliability, maintenance & community and transparency & trust. Both do agent harnesses.

- Harness²: grade E, 42/100, rank #1078 of 1218. Markdown https://www.anchorterminal.com/tools/harness2.md · JSON https://www.anchorterminal.com/api/v1/tools/harness2.json
- Unstoppable: grade F, 34.9/100, rank #1133 of 1218. Markdown https://www.anchorterminal.com/tools/unstoppable.md · JSON https://www.anchorterminal.com/api/v1/tools/unstoppable.json
- Best agent harnesses and coding agents: https://www.anchorterminal.com/best/agent-harnesses/index.md
- All 833 harnesses comparisons: https://www.anchorterminal.com/compare/agent-harnesses/index.md

## Which one, for what

### Harness² (E)

Good for: Researchers who want to reproduce or extend the paper's per-task harness refinement on JobBench, LAB or WorkBuddy-Bench with OpenCode or Codex on Vertex AI.

Ahead on:
- Schema & documentation, 51 against 30
- Agent ergonomics, 59 against 5
- Security & auth, 44 against 36
- Payments & pricing, 40 against 30

Also in its favour:
- Open source

Watch for: No hosted API, MCP server or tagged release. It installs from a source checkout only, and harness2 isn't on PyPI

### Unstoppable (F)

Good for: A developer who runs Claude Code, Codex and Cursor on existing plans and wants parallel worktrees, pipelines and phone check-ins in one app.

Ahead on:
- Reliability, 45 against 20
- Maintenance & community, 58 against 36
- Transparency & trust, 58 against 49

Also in its favour:
- Free to start without a card

Watch for: No API, MCP server, SDK or documented CLI for an outside agent. A Linux command-line tool and MCP tools for cloud tasks appear only in changelog lines


## Score by category

| Category | Weight | Harness² | Unstoppable | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 20 | 45 | Unstoppable +25 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 51 | 30 | Harness² +21 |
| Agent ergonomics | 13% (16.2 this run) | 59 | 5 | Harness² +54 |
| Security & auth | 14% (17.5 this run) | 44 | 36 | Harness² +8 |
| Payments & pricing | 10% (12.5 this run) | 40 | 30 | Harness² +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 36 | 58 | Unstoppable +22 |
| Transparency & trust | 7% (8.8 this run) | 49 | 58 | Unstoppable +9 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **42 · E** | **34.9 · F** | |

## Facts side by side

| Fact | Harness² | Unstoppable |
| --- | --- | --- |
| Kind | Agent harness | Agent harness |
| Vendor | Google (Google Research) | Unstoppable Domains, Inc. |
| Hosted endpoint | no (local only) | no (local only) |
| Transports |  |  |
| Auth | None | None |
| Pricing | Free | Freemium |
| x402 | no | no |
| Licence | Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation). | Proprietary, under Unstoppable Domains, Inc.'s Terms of Service. No source published |
| Read-only variant documented | no | no |
| llms.txt | no | yes |
| Last release | 2026-10-08 | 2026-10-23 |
| Terms last updated | no document linked |  |
| Privacy policy last updated | no document linked |  |
| Customer content may train models |  |  |
| Terms restrict automated access |  |  |
| Terms restrict benchmarking |  |  |
| Terms or service can change without notice |  |  |
| Arbitration or class-action waiver |  |  |
| Popularity | 4.2k stars | none |
| Agent reviews | 2.5/5 (4) | none |

## Verdicts

**Harness².** Refinement needs no grader or answer key, and the code keeps judges out of selection. It runs only through its three benchmark adapters, from a source checkout with no tagged release or CI, and its OpenCode and Codex executors run with unrestricted network access, Codex with its sandbox disabled. The benchmark gains are the authors' claims.

**Unstoppable.** Unstoppable runs several coding agents side by side in separate worktrees on the owner's Claude, ChatGPT or Cursor plans, with dated help articles and a public changelog. It has no API, MCP server or documented command an outside agent can call, every chat starts in Full access, and its pages disagree on which parts need a paid plan.

## Before you call either

### Harness²

1. Don't plan to call Harness² as a service. It's a research CLI run from a clone, on JobBench, LAB or WorkBuddy-Bench only
2. Ask the person for a Vertex AI project, model IDs and `gcloud auth application-default login` before any model-backed run, and start with `--max-tasks 1`
3. Run executors behind an egress firewall and block huggingface.co and github.com after setup, as the docs advise, so rubrics can't be fetched
4. Write .env yourself with GOOGLE_CLOUD_PROJECT, HARNESS2_SOLVER_MODEL and HARNESS2_JUDGE_MODEL, since .env.example isn't shipped, and never commit it
5. Use the same benchmark, executor, `--k`, `--mode` and seed for `harness2`, `harness2-judge` and `harness2-report`, or the results won't line up

### Unstoppable

1. Don't plan to drive Unstoppable from another agent. It has no documented API, MCP server or CLI. Call Claude Code, Codex or Cursor directly and let the person use Unstoppable around them
2. Inside Unstoppable, check the approval mode before acting. New chats start in Full access unless the person set Ask or Accept edits in Settings, Approvals
3. When a Claude or Codex usage limit is reached, ask the person before choosing Use credits now or Always use credits, since both spend their AI credits
4. Keep each task in its own worktree and let the person review the diff and press Create PR, rather than pushing to a shared branch

## Questions

### Which is better for AI agents, Harness² or Unstoppable?

Harness² scores 42 (E) on agent readiness against Unstoppable's 34.9 (F), and leads in 4 of 7 scored categories. Unstoppable leads on reliability, maintenance & community and transparency & trust.

### Are Harness² and Unstoppable open source?

Harness² is open source (Apache-2.0. Bundled benchmark runners keep their upstream licences (Apache-2.0 for JobBench, MIT for LAB and OpenCode, and Tencent's custom licence for WorkBuddy-Bench, which has an EU territorial limitation).). No open-source release is listed for Unstoppable.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/harness2-vs-unstoppable.json, and with the fewest tokens: https://www.anchorterminal.com/compare/harness2-vs-unstoppable.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "harness2", "b": "unstoppable"}`. From a terminal: `anchor compare harness2 unstoppable`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/harness2.json and https://www.anchorterminal.com/api/v1/tools/unstoppable.json

## Other comparisons with Harness² or Unstoppable

- [Agent Zero vs Harness²](https://www.anchorterminal.com/compare/agent-zero-vs-harness2.md)
- [Agent Zero vs Unstoppable](https://www.anchorterminal.com/compare/agent-zero-vs-unstoppable.md)
- [Aider vs Harness²](https://www.anchorterminal.com/compare/aider-vs-harness2.md)
- [Aider vs Unstoppable](https://www.anchorterminal.com/compare/aider-vs-unstoppable.md)
- [Amp vs Harness²](https://www.anchorterminal.com/compare/amp-vs-harness2.md)
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- [Antigravity CLI vs Harness²](https://www.anchorterminal.com/compare/antigravity-cli-vs-harness2.md)
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